Proof found of bone disease in early mammals

UCT researchers have discovered bone disease in a 265 million-year-old mammal ancestor. Experts at UCT’s Biological Sciences department found an unusual bone tissue pattern that was suspected to be osteomyelitis, an infection of the bone, in the femur of an omnivorous therapsid, more specifically known as a dinocephalian.

According to the New World Encyclopedia, therapsids are “mammal-like reptiles” that flourished between 275 and 205 million years ago and are thought to have been the precursors of mammals. Aside from the mammals, all of the other lines of descent from the therapsid ancestors have become extinct.

Osteomyelitis is a degenerative bone disease caused by a bacterial infection that eats away bone.

Christen Shelton of UCT’s Biological Science department and first author of a paper documenting the find, published in the International Journal of Paleobiology, Historical Biology, said: “While analysing thin sections of the femur under a microscope, I noticed that the bone tissue did not follow the normal growth pattern as that observed in other specimens.”

The earliest occurrence of this disease was discovered in the backbone of the iconic dorsal sailed pelycosaur.

This “mammal-like reptile” lived 280 million years ago and was part of a group that gave rise to the mammals we know today. Linking modern mammals and pelycosaurs is another group of advanced “mammal-like reptiles” known as the therapsids. Until now, osteomyelitis was assumed to exist in this group of mammal-like reptiles as well, but

On the femur were puncture marks and the bite became infected.

no proof had ever been found.

Shelton suspected the find was something special and sought expert advice from Professor Anusuya Chinsamy, a palaeobiologist at UCT.

She agreed that this was unusual, pointing out areas of the bone tissue that showed some bone layers growing perpendicular to each other.

Chinsamy said: “This pattern is often indicative of a pathology, something that either damaged or disrupted the normal bone tissue growth. Researchers have long assumed that osteomyelitis must have occurred in therapsids, but now we can back up those assumptions with histological proof.”

Bruce Rothschild of the West Virginia University School of Medicine, who has worked extensively researching bone pathologies in dinosaurs, joined the team of researchers and identified that the unusual bone pattern was due to a bacterial infection and the animal’s response to it.

“This made sense because on the femur we found two teeth puncture marks, which we believe resulted from a bite by a predator during its lifetime.

“This potential bite became infected and resulted in the pathology we discovered here,” Shelton said.